How to change frequency in Sierra GSM modems

This guide will help you change the frequency when you
use a Sierra Fastrack GSM modem. It is useful if your service provider use
another frequency than 900/1800 MHz. In this guide you can see how to change
the frequency from 900/1800 MHz to 850/1900 MHz. However, other options are also listed
in the tables below.

If you use GSM modem for connecting to the mobile network,
it can occur that your service provider uses other frequency than the default
frequency in the Sierra modem. This default frequency in Sierra Fastrack Xtend
GSM modems is 900/1800 MHz.

So before you start to use the GSM modem it is highly recommended to ask your
service provider about the used frequency. If they use other frequency than
the default 900/1800 MHz, you need to set the GSM modem to the used frequency.

Sierra Fastrack Xtend modems supports the following frequencies: 850, 900, 1800,
1900. You can set the frequency by using AT commands in the modem.

It is assumed that Ozeki NG SMS Gateway and a Sierra Fastrack Xtend modem
has already been installed to your PC.

First, please stop the Ozeki NG SMS Gateway service by clicking on Stop
service (Figure 1).

Figure 1 - Stop Ozeki service

On Figure 2 you can see the message if the Ozeki NG SMS Gateway
software has stopped.

Figure 2 - Ozeki NG SMS Gateway stopped

Now start Hyperterminal at
Start / Accessories / Communications / Hyperterminal (Figure 3). Please note that
if you use Windows Vista or newer operating system, you need to download
Hyperterminal. You can download Hperterminal from the following website:
http://www.hilgraeve.com/htpe/download.html

Figure 3 - Start Hyperterminal

Create a new connection and provide a name for this connection
(Figure 4). Click on OK

Figure 4 - New connection name

Select the port that is used by the GSM modem at Connect using
drop down menu (Figure 5).

Figure 5 - Select the port

Select the speed at Bits per second drop down menu. Set
it to 115200 (Figure 6). Click on OK.

Figure 6 - Set the speed

Check if the connection is successful by typing at command into
Hyperterminal. If it returns OK, the connection is successful (Figure 7).

Figure 7 - Connection is successful

Now issue at+wmbs? command to check the frequency. The return
values of this command can be the follows:

Return values for at+wmbs? command:

Return value

Description

+WMBS: 0,x

Mono band mode 850 MHz is selected

+WMBS: 1,x

Mono band mode extended 900 MHz is selected

+WMBS: 2,x

Mono band mode 1800 MHz is selected

+WMBS: 3,x

Mono band mode 1900 MHz is selected

+WMBS: 4,x

Dual band mode 850/1900 MHz is selected

+WMBS: 5,x

Dual band mode extended 900/1800 MHz is selected

+WMBS: 6,x

Dual band mode extended 900/1900 MHz is selected

As you can see at Figure 8 the GSM modem returns +WMBS: 5,0 meaning that
it uses 900/1800mhz by default.

Figure 8 - Check the frequency

If you issue at+wmbs=4,1 the frequency will be change to
850/1900mhz. If OK is returned the change has been successful (Figure 9).

Possible Commands:

Command

Description

AT+WMBS=0,x

Select mono band mode 850 MHz

AT+WMBS=1,x

Select mono band mode extend 900 MHz

AT+WMBS=2,x

Select mono band mode 1800 MHz

AT+WMBS=3,x

Select mono band mode 1900 MHz

AT+WMBS=4,x

Select dual band mode 850/1900 MHz

AT+WMBS=5,x

Select dual band mode extend 900/1800 MHz

AT+WMBS=6,x

Select dual band mode extend 900/1900 MHz

Remark:

x=0 : The Plug & Play will have to be reset to start on specified band(s).

x=1 : The change is effective immediately. This mode is forbidden while
in communication and during Plug & Play initialization.

Figure 9 - Change frequency

You can also check of the change has been successful by
at+wmbs? command. If the return value is +WMBS: 4,0 then the
the frequency has been set to 850/1900 MHz successfully (Figure 10).

Figure 10 - Check the changed frequency

You can also check the changed frequency by at+cgmm
command. In this case the frequency will be shown in text: MULTIBAND G850 1900
(Figure 11).